STRATIFIED SQUAMOUS EPITHELIUM

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The number of layers in this type of epithelium varies considerably in different locations but the shape and arrangement of the cells are quite characteristic. The deepest or basal layer which rests on a basement membrane is formed by low columnar or cuboidal cells which steadily divide mitotically to provide a constant supply of cells for the overlying layers. Next to the basal layer are present a few layers of larger polygonal cells.

Stratified Squamous Epithelium 

As the free surface is approached the cells gradually become flattened and at the surface they assume a squamous 'flat' shape. The condition of the cells of the most superficial layers of the stratified squamous epithelium varies with the location and environment of the epithelium.
Two subvarieties of the stratified squamous epithelium are recognized:
  •     Kratinized (also called cornified)                 
  •     Nonkeratinized (also called noncornified)

KRATINIZED

 The stratified squamous keratinized epithelium covers those areas of the body which are subjected to abrasion and desiccation '' drying '' . In this type of epithelium, the cytoplasm of the superficial cells accumulates large numbers of keratin filaments. Near the surface of the epithelia the cells lose their nuclei and organelles and become converted into dead, flattened plates consisting of the protein keratin. The intercellular space between the squamous cells contains a water proofing glycolipid. The best example of the stratified squamous keratinized epithelium is the epidermis

Stratified squamous keratinized epithelium 


 which covers the entire free surface of the body.

Found In:

  • Epidermis 
  • Opening of body cavities 
  • Urethra, Vagina and anal canal


NON-KERATINIZED

     The stratified squamous nonkeratinized epithelium lines those slippery surfaces in the body which are subjected to abrasion but remain wet. In this variety of the stratified squamous EPITHELIUM. The surface cells become very flat but mostly remain nucleated and their cytoplasm contains little or no keratin.

Stratified Squamous Nonkeratinized Epithelium 

The lining epithelia of most of the

  •  Oral cavity
  •  Oropharynx 
  •  Esophagus 

 belong to the stratified squamous nonkeratinized variety. In both subtypes of the stratified squamous epithelium the most superficial cells constantly flake off from the surface, indicating the base to surface progress of the cells. As already noted, mitotic activity in the basal layer produces new cells which move into the overlying layers and become polygonal in shape. In the polygonal cell layers, the cells still keep on moving toward the surface until they reach the most superficial layers where they assume a squamous shape. The most superficial squamous cells lose their desmosomes and flake off from the free surface.

Found In:

  • In musle members of cavities
  • Pharynx
  • Esophagus 
  • Urethra some parts


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